1. Field of the Invention
The present invention relates to telephone systems in general and to Intelligent Network (IN), Advanced Intelligent Network (AIN) systems and Computer Telephony Integration (CTI) in particular. More particularly still, it relates to telephone number portability, also known as local number portability (LNP) within such systems. More particularly yet, it relates to an intermediate service management system (SMS) architecture advantageous for LNP.
2. Prior Art of the Invention
North American Numbering Plan defines a telephone number as NPA-NXX-XXXX, (a glossary of abbreviations is found in the Appendix attached to this specification), where NPA are three digits which define the area code of the telephone subscriber, NXX indicates the switching exchange or switch where the subscriber is served. N represents a digit from 2 to 9 and X represents a digit from 0 to 9. The NPA has the NXX format.
A set of requirements has been defined for local Number Portability that defines the functionality for SSP (switches) STPs, SCPs, NPACs and L-SMS as well as the interfaces between these elements. These requirements describe how the LRN method uses AIN to a central LNP database (e.g. SCP) to access routing information for telephone numbers in areas where Number Portability occurs. A typical call flow in conformance with such requirements runs as follows:
1. Line A (708-224-1111) dials Line B (708-713-2222). PA1 2. The Originating Switch performs digit analysis on the dialed digits to determine how to route the call. The switch determines that B is in a portable NPA-NXX (708-713) and the line does not reside on the switch. PA1 3. The switch sends an AIN (info.sub.-- Analyzed) or IN (InstructionStart) query based on the dialed digits to the LNP-SCP. PA1 4. The LNP-SCP sends an AIN (Analyze.sub.-- Route) or IN (ControlConnect) response containing the LRN of the Recipient Switch. PA1 5. The Originating Switch receives the LNP-SCP response and analyzes the data. The LRN is translated in the LNP Routing Tables and an ISUP route out of the switch is determined. The LRN is stored in the CdPN parameter and the dialed digits are stored in the GAP parameter of the ISUP IAM message. The FCI Translated Called Number Indicator is set to indicate a query has been done (set to "translated number"). PA1 6. The call is routed to the Recipient Switch based on the LRN. PA1 7. The Recipient Switch receives and processes the contents of the IAM message. The switch determines than an LRN is received and that it is the switch's LRN, and the switch replaces the CdPN parameter's contents with the dialed digits stored in the GAP parameter. The switch does digit analysis on the dialed digits and finds the subscriber on the switch. PA1 8. The Recipient Switch completes the call to the subscriber. PA1 (a) a plurality of databases at said S-SMS intermediate, a number portability administration center (NPAC) and a switching office; PA1 (b) means at said S-SMS for downloading ported telephone numbers from said NPAC into said databases; and PA1 (c) means at said S-SMS for downloading selected ones from said ported telephone members into an LNP-database in said switching office. PA1 (a) maintaining a plurality of databases at said S-SMS intermediate, a number portability administration center (NPAC) and a switching office; PA1 (b) downloading ported telephone numbers from said NPAC into said databases; PA1 (c) selecting telephone numbers that have been ported from said switching office from said ported telephone numbers; and PA1 (d) storing the telephone numbers selected in step (c) for storage in an LNP database in said switching office.
This implementation relies heavily on the IN or AIN technology and is not efficient, since it is a complex protocol that must communicate across network elements while a call is in active progress.
U.S. Pat. No. 5,625,681 to Stratus "Method and Apparatus for Telephone Number Portability" relies on the AINs SCP, although it is somewhat short on implementation detail.